This invention relates in general to thrust washers that are disposed between the outer ends of trunnions and the inner surfaces of bearing cups in universal joint assemblies. More specifically, this invention relates to an improved structure for such a thrust washer including inner and outer regions that are formed from two different types of materials and that are connected together by one or more legs.
In most land vehicles in use today, a drive train assembly is provided for transmitting rotational power from an output shaft of an transmission to an input shaft of an axle assembly so as to rotatably drive one or more wheels of the vehicle. To accomplish this, a typical vehicular drive train assembly includes a hollow cylindrical driveshaft tube. A first universal joint is connected between the output shaft of the transmission and a first end of the driveshaft tube, while a second universal joint is connected between a second end of the driveshaft tube and the input shaft of the axle assembly. The universal joints provide a rotational driving connection from the output shaft of the transmission through the driveshaft tube to the input shaft of the axle assembly, while accommodating a limited amount of angular misalignment between the rotational axes of these three shafts.
A typical universal joint includes a cross having a central body portion with four cylindrical trunnions extending outwardly therefrom. The trunnions are oriented in a single plane and extend at right angles relative to one another. A hollow cylindrical bearing cup having a cylindrical outside wall and a circular end wall is mounted on the end of each of the trunnions. A bearing structure, such as a plurality of needle bearings or roller bearings, is provided between the trunnion and the associated bearing cup to facilitate relative rotational movement therebetween. The bearing cups that are mounted on a first opposed pair of the trunnions can be connected to a first yoke secured to a first component of the drive train assembly, while the bearing cups mounted on a second opposed pair of the trunnions can be connected to a second yoke secured to a second component of the drive shaft assembly.
When the bearing cups are mounted on the associated trunnions, the circular end walls of the bearing cups are disposed adjacent to the axially outer ends of the trunnions and bearings. If the inner surfaces of these end walls directly contact the axially outer end surfaces of the trunnions during operation, friction caused by such direct contact can generate undesirable heat and wear. However, if the inner end surfaces of the bearing cups do not fit snugly against the axially outer end surfaces of the trunnions, relative axial movement between the bearing cups and the trunnions can cause imbalances and result in undesirable noise and vibrations. Thus, to address these situations, it is known to position a thrust washer between the inner end surface of the bearing cup and the axially outer end surface of the trunnion. A typical thrust washer is formed from a relatively low friction, wear resistant material, such as plastic, that can absorb the thrust loads that occur between the end of the trunnion and the bearing cap and take up any looseness therebetween. A typical thrust washer also extends radially outwardly into the annular space between the axially outer ends of the bearings and the end wall of the bearing cup to properly position such bearings relative to the bearing cup during operation.
In the past, such thrust washers have been manufactured from a single annular piece of material having a first inner portion that extended between the axially outer end of the trunnion and the end wall of the bearing cup and a second outer portion that extended between the axially outer ends of the bearings and the end wall of the bearing cup. This structure performs well for most applications of universal joint assemblies. However, problems can occur when universal joint assemblies having unitary thrust washers are used in high speed, high angle, and low torque applications. In these situations, the trunnion may become angled relative to the bearing cup and apply uneven pressure against the first portion of the thrust washer. When this occurs, one side of the first portion of the thrust washer is forced against the bearing cup, while the other side moves away from the bearing cup. Because the first and second portions of the thrust washer are formed as a single piece of material, the corresponding side of the second portion of the thrust washer also moves away from the bearing cup. When the ends of the needle bearings engage this side of the thrust washer, the thrust washer is subjected to significant wear and may eventually break apart.
In these situations, it would be desirable to form the first and second portions of the thrust washer as separate members. At the same time, because the first and second portions of the thrust washers are intended to address different aspects of operation of the universal joint, it would be desirable to form the first and second portions of the thrust washers from two different materials. However, the use of two separate thrust washer portions creates increased difficulty in manufacturing the universal joint, both in the increased number of parts that must be handled during assembly and in the increased likelihood that one or both of the thrust washer portions may become dislodged or otherwise improperly positioned during assembly. Thus, it would be desirable to provide an improved structure for a thrust washer for use in a universal joint assembly that addresses these concerns.